1. Field of the Invention
The present invention relates to a rewritable optical recording medium, and more particularly, to a method for controlling track jump in an optical recording medium having land and groove tracks with depths different from each other in a direction of a beam.
2. Background of the Related Art
In general, an optical recording medium system, i.e., an optical disk recording/reproducing device is a device for reading a data recorded on an optical disk, such as CD (Compact Disk) or DVD(Digital Versatile Disc), or writing the data on the optical disk. Of the rewritable optical disk in the optical disk, there are CD-RW(Rewritable Compact Disc), and Rewritable Digital Versatile Discs(DVD--RW, DVD-RAM, DVD+RW). Particularly, the DVD-RAM has signal tracks of lands and grooves, to write or read data to/from tracks, not only of lands or grooves, but also tracks both of lands and grooves.
FIG. 1 illustrates a block diagram of a related art recording/reproducing device such a DVD-RAM, wherein, under the control of the servo controller 113, an optical pickup 102 directs a beam focused by an objective lens onto the signal track of the optical disk 101, or directs a beam, reflected at a signal recording surface and focused again by the objective lens, toward an optical detector for detecting a focus error signal and a tracking error signal. The optical detector has a plurality of optical detecting elements each for forwarding an electric signal proportional to an optical quantity of light incident thereto to a RF and servo error generator 103. As shown in FIG. 2, if the optical detector has a particular number of divisions, i.e., four divisions in a signal track direction and in a radial direction of the optical disk 101, four optical detecting elements PDA, PDB, PDC, and PDD, the optical detector forwards electrical signals `a`, `b`, `c`, and `d` proportional to quantities of lights obtained at respective optical detecting elements PDA, PDB, PDC, and PDD to the RF and servo error generator 103. The RF and servo error generator 103 combines the electrical signals `a`, `b`, `c`, and `d`, to produce a RF signal (or a read channel 1 signal) required for data reproduction, a read channel 2 signal required for servo control, and a focus error signal. The RF signal can be obtained by (a+b+c+d) of the electrical signals from the optical detector, the read channel 2 signal can be obtained by (a+d)-(b+c) of the electrical signals from the optical detector, and the tracking error TE signal can be obtained by processing the read channel 2 signal. If the optical detector has two division in the track direction, the RF signal (=I1+I2) and the read channel 2 signal (=I1-I2) can be detected from balances of quantities of lights. That is, `a`+`d` in FIG. 2 corresponds to I1, and `b`+`c` corresponds to I2. In this instance, in a case of a rewritable disk 101, it is impossible to control and write on the disk because the disk has no information. For this, by forming disk tracks on the lands and the grooves, writing information along the tracks, and writing control information on sector addresses, random accesses, and rotation control separately, the tracking control can be made even for an empty disk having no information signal recorded thereon. The control information may be written by pre-formatting a header region at beginning of every sector. In a case of the DVD-RAM, the head region pre-formatted at beginning of every sector is provided with four header fields(a header 1 field.about.header 4 field) again. The header 1, and 2 fields and the header 3 and 4 fields are formed to alternate with reference to a track center, one example of which is illustrated in FIG. 3 wherein a configuration of a header field for the first sector of one track is shown.
However, the header configuration affects generation of servo error signals, such as the tracking error signal, focus error signal actually. That is, the servo error signal read from the header region is distorted by the header configuration, control of which is difficult. Therefore, in the case of the DVD-RAM, in order to generate the servo signal and to make a stable control of it, the servo is controlled by holding respective error signals, for example, the tracking error TE signal and the focus error FE signal for reducing an influence from the header. That is, a focus sample & hold part 104 samples and holds the focus error FE signal and the tracking error TE signal at positions right forward of the header region. This is because, though the focus servo and the tracking servo operations are carried out even in the header, the servo operations are carried out, not by the tracking error signal and the focus error signal detected in the header region, but by the tracking error signal and the focus error signal held at the positions right forward of the header region. In this instance, the header region may be detected by different methods including known arts.
In the meantime, the tracking error signal on the land is an inversion of the tracking error signal in the groove. That is, since the tracking error signal detected from the land has a phase inverted from a phase of the tracking error signal detected from the groove, the phases of the tracking error signals both from the land and the groove should be made the same for making regular tracking on the land and groove. And, there is a difference of DC offsets the land and the groove basically have (i.e., a difference of amounts in terms of signals coming from a depth difference of the land and the groove). That is, even if the focusing and the tracking are right on the land track, if the focusing and the tracking are applied to the groove track as they are, a defocusing and a detracking may occur, and, opposite to this, even if the focusing and the tracking are right in the groove track, if the focusing and the tracking are applied to the land track as they are, the defocusing and the detracking may occur due to a difference of depth between the land and the groove. Therefore, an additional circuit for this is required, such as a focus groove offset part 105, a focus land offset part 106, a tacking groove offset part 109, and a tracking land offset part 110. The focus groove offset part 105 and the focus land offset part 106 adjust focus error offsets of the groove/land respectively for carrying out a regular focus servo. And, the tacking groove offset part 109, the tracking land offset part 110, and the invertor 111 adjust tracking errors for the groove/land respectively and inverts the tracking error signal detected from the land for carrying out regular tracking servo.
In this instance, L/G selecting part 107 or 112 selects the focus error signal and the inverted tracking error signal having offsets adjusted respectively to be consistent to the land at the land offset part 106 or 110 in response to an L/G switching signal L/Gsw, i.e., if the present signal track represents the land, or, the L/G selecting part 107 or 112 selects the focus error signal and the tracking error signal having offsets adjusted respectively to be consistent to the groove at the groove offset part 105 or 109 in response to an L/G switching signal L/Gsw, i.e., if the present signal track represents the groove, and forwards the selected focus error signal and the tracking error signal to the servo controller 113. Accordingly, the servo controller 113 conducts the focus servo and the tracking servo either by using the focus error signal and the tracking error signal having offsets adjusted respectively to be consistent with the land through an F/T(Focus/Track) servo driver 114, or by using the focus error signal and the tracking error signal having offsets adjusted respectively to be consistent with the groove through an F/T(Focus/Track) servo driver 114, in response to the L/G switching signal L/Gsw. The L/G denotes a switching from the land signal track to the groove signal track or vice versa.
Such an L/G switching signal L/Gsw is generated at the L/G switching signal generator 117. The L/G switching signal generator 117 is provided with L/G determining part 118 for determining the land and the groove by using IP1 and IP2 signals detected from the read channel 2 signal, and an L/G switching signal forwarding part 119 for inverting the L/G switching signal L/Gsw according to the L/G determination result.
FIGS. 4A.about.4C illustrate waveforms showing a process of generating the L/G switching signal L/Gsw of L/G switching in a regular servo, i.e., in regular writing/reading. That is, the read channel 2 signals detected in the header 1, 2 fields and the header 3, 4 fields have opposite phases (i.e., slopes) because the header region, i.e., the header 1, 2 fields and the header 3, 4 fields are arranged to alternate with reference to a track center. Therefore, if the read channel 2 signal is sliced at a preset slice level, the IP1 and the IP2 can be detected. For example, if it is assumed that the slice level is set to the track center, and the IP1 signal is generated if the read channel 2 signal is higher than the slice level, and the IP2 signal is generated if the read channel 2 signal is lower than the slice level, phases of the IP1 signal and the IP2 signal will be changed depending on the track tracking at the present time of being the land or the groove. Dependent on the land/groove track, either the IP1 signal or the IP2 signal comes the first. Therefore, as shown in FIG. 4A, the L/G determining part 118 determines a front and a rear of the IP1 and IP2 signals detected at every header position, to invert ipLG signal as shown in FIG. 4B, and the L/G switching signal forwarding part 119 inverts the L/G switching signal L/Gsw as shown in FIG. 4C and forwards to a microcomputer 116 and the L/G selecting parts 107 and 112 if the ipLG signal is switched. That is, the L/G determining part 118 determines the optical pickup 102 of tracking the land track or the groove track with reference to the IP1 and IP2 signals, and forwards a relevant signal ipLG, and the L/G switching signal forwarding part 119 forwards a signal L/Gsw for controlling the optical pickup 102 to track the land track or the groove track.
The description until now is on regular servo, i.e., regular writing/reading in an L/G structured DVD-RAM. If the foregoing method is applied to a track jump in the DVD-RAM, there can be a problem. That is, in a case of the L/G structured DVD-RAM, if odd numbers of track jumps inclusive of one track jump, for example, track jumps of land.fwdarw.groove, or groove.fwdarw.land are done, a land and groove inversion is occurred, to require the L/G switching. However, in the track jump, detection of the read channel 2 signal is poor because the turned off tracking servo causes the servo unstable, that results in poor detection of the IP1 and IP2 signals too, to fail proper generation of the ipLG signal. The improper ipLG signal may switch the L/G switching signal LGsw at a section which is not a L/G switching time point. And, if the offset is not exact due to this, a defocus or detrack may occur, in which the focus or the tracking servo does not follow a desired track. And, if no L/G switching is made in the odd number track jump, with the L/G signal having a previous value as it was, the defocus, or the detrack is occurred, in which the tracking servo does not follow a desired track, but to a track at a side of the desired track because the offsets are not exact. That is, in a jump of land.fwdarw.groove track, the focusing, and tracking may follow, not a groove track, but a land track, and, opposite to this, in a jump of groove.fwdarw.land track, the focusing and tracking may follow, not a land track, but a groove track. Particularly, if the foregoing related art is used in one track jump in an optical disk, such as the DVD-RAM data writing/reading both on/in land/groove of which is permitted as it is, there is a possibility of occurrence of two track jump. That is, provided that one track jump command is given, the servo controller 113 generates a kick pulse (or a jump pulse) in a state only the focus servo is turned on, and provides a track driving voltage TAO proportional to the kick pulse to a tracking actuator through an F/T servo driver 114 as shown in FIG. 5C. When the track driving voltage TAO proportional to the kick pulse is provided, an object lens of the tracking actuator is pushed in a direction of track jump by an acceleration as a speed of the tracking actuator is increased. In this instance, the tracking error signal makes an `S` curve as shown in FIG. 5A. And, as shown in FIG. 5B, a TZC(Track Zero Crossing) signal turned on/off at a zero cross time point of the tracking error signal TE rises at a zero cross position of the tracking error signal. When the TZC signal rises, the servo controller 113 applies brake pulses to the actuator for a preset brake time period, to drop a speed of the actuator. That is, the tracking actuator is accelerated by the kick pulse until the brake pulse is generated when the tracking actuator is decelerated. Being inverted pulses of the kick pulses, the brake pulses are generated for stable and exact stopping of the actuator at a desired position. And, at an end of the preset brake time period, the tracking servo and a sled servo are turned on, to complete the track jump.
In a case when the optical disk 101 is a disk data can be written either on a track or in a groove thereof, such as CD-ROM, DVD-ROM, if the track jump is done by the foregoing process, one track jump is made. However, if the optical disk 101 is a disk data can be written/read both on the land and in the groove, for example, the DVD-RAM, if the track jump is done by the foregoing process, two track jump is made. That is, not one track jump of groove.fwdarw.land, or land.fwdarw.groove, but two track jump of groove.fwdarw.groove, or land.fwdarw.land is made.